Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$178.74	3.795%	$185.5232	$185.52	$185.50	$185.50
Purchase #2	$139.73	13.520%	$158.6215	$158.62	$158.60	$158.60
Purchase #3	$82.91	3.345%	$85.6833	$85.68	$85.70	$85.70
Purchase #4	$130.71	13.229%	$148.0016	$148.00	$148.00	$148.00
Purchase #5	$175.38	13.150%	$198.4425	$198.44	$198.45	$198.40
Purchase #6	$27.82	12.442%	$31.2814	$31.28	$31.30	$31.30
Purchase #7	$158.26	11.470%	$176.4124	$176.41	$176.40	$176.40
7 purchase totals =	$893.55		$983.9659	$983.95	$983.95	$983.90